We report an electrode-free photovoltaic experiment in epitaxial BiFeO 3 thin films where the picosecond optical absorption arising from carrier dynamics and piezoelectric lattice distortion due to the photovoltaic field are correlated at nanoscale. The data strongly suggest that the photovoltaic effect in phase-pure BiFeO 3 originates from diffusion of charge-neutral excitons and their subsequent dissociation localized at sample interfaces. This is in stark contrast to the belief that carrier separation is uniform within the sample due to the lack of center of symmetry in BiFeO 3. As a result, this finding is important for formulating strategies in designing practicalmore » photovoltaic ferroelectric devices.« less

Self-poling of ferroelectric films, i.e., a preferred, uniform direction of the ferroelectric polarization in as-grown samples is often observed yet poorly understood despite its importance for device applications. The multiferroic perovskite BiFeO 3, which crystallizes in two distinct structural polymorphs depending on applied epitaxial strain, is well known to exhibit self-poling. This study investigates the effect of self-poling on the monoclinic domain configuration and the switching properties of the two polymorphs of BiFeO 3 (R' and T') in thin films grown on LaAlO 3 substrates with slightly different La 0.3Sr 0.7MnO 3 buffer layers. Our study shows that the polarizationmore » state formed during the growth acts as “imprint” on the polarization and that switching the polarization away from this self-poled direction can only be done at the expense of the sample's monoclinic domain configuration. We observed reduction of the monoclinic domain size and found that it was largely reversible; hence, the domain size is restored when the polarization is switched back to its original orientation. This is a direct consequence of the growth taking place in the polar phase (below T c). Finally, switching the polarization away from the preferred configuration, in which defects and domain patterns synergistically minimize the system's energy, leads to a domain state with smaller (and more highly strained and distorted) monoclinic domains.« less